Flat-panel displays are widely used in conjunction with computing devices, in portable devices, and for entertainment devices such as televisions. Such displays typically employ an array of pixels distributed in rows and columns over a display substrate to display images, graphics, or text. In a color display, each pixel includes light emitters that emit light of different colors, such as red, green, and blue. For example, liquid crystal displays (LCDs) employ liquid crystals to block or transmit light from a backlight behind the liquid crystals and organic light-emitting diode (OLED) displays rely on passing current through a layer of organic material that glows in response to the current. Displays using inorganic light emitting diodes (LEDs) are also in widespread use for outdoor signage and have been demonstrated in a 55-inch television. Flat-panel electronic sensors having a plurality of pixel sensors are also available, for example for digital radiography.
Pixels in a display are typically arranged in an array of rows and columns and controlled through a matrix-addressing scheme in which rows of pixels are connected to a common row-select line and columns of pixel are connected to a common column-data line. By enabling a row of pixels and providing data on all of the column-data lines at the same time, all of the pixels in a row receive data at the same time. Each row of pixels is sequentially enabled to provide data to all of the display pixels in sequence. The row-select lines are typically controlled by a row controller and the column-data lines by a column controller. This arrangement, however, requires a separate electrical connection for each column and for each row. Thus, for an M×N pixel array, M+N electrical connections must be made to the array of pixels and generally to the substrate on which the flat-panel display is provided. For large displays, for example having thousands of rows and columns of pixels, the cost of connecting the pixel rows and columns can be significant.
Large-format displays, for example having a diagonal greater than 3 meters, are typically made with a two-dimensional array of tiles. Each tile includes a contiguous two-dimensional subset of the pixels in the display. Wires connect each tile to a system controller. The number of wires, interconnections, and the electronics to support each display tile are expensive and problematic. Alternatively, U.S. Pat. No. 6,999,045 discloses an electronic system for tiled displays that includes display tiles serially connected through communication interfaces and one display tile connected to a system controller. This approach requires high-performance integrated circuits distributed among the display tiles and is difficult to implement with conventional thin-film transistor (TFT) display backplanes, especially for high-resolution displays, since TFT circuits are large and have relatively low performance.
A significant and common problem for tiled displays are visible seams between the tiles that detract from the display image quality. Display tiles are typically butted together mechanically in a two-dimensional array and the supportive mechanical structures for the tiles can be visible and can also limit the resolution of the display. Moreover, as displays increase in resolution, the area between the pixels decreases, reducing the space at the edges of the display tiles for the supportive tile structures. Furthermore, electronic control circuitry to drive the pixels in a display (e.g., the row and column drivers) are typically located at two sides of the display area. Thus, simply arranging an array of conventional displays creates gaps between pixels at the edges of the display. U.S. Pat. No. 7,394,194 describes a tiled display with back-panel conductors that seeks to mitigate this problem by locating pixel control electronics behind the pixels. U.S. Patent Application Publication No. 2006/0044215 and U.S. Pat. No. 8,305,294 describe displays with overlapping tiles to obscure the electronic row and column driver circuitry. However, these approaches require a stacked layer structure and electrical connections between the layers.
Many large-format displays use inorganic light-emitting diodes (iLEDs) in the display pixels. However, such iLEDs are typically large and further limit the display resolution. Micro-LEDs are known that have an area less than 1 mm square, less than 100 microns square, or less than 50 microns square or have an area small enough that it is not visible to an unaided observer of the display at a designed viewing distance. U.S. Pat. No. 8,722,458 entitled Optical Systems Fabricated by Printing-Based Assembly teaches transferring light-emitting, light-sensing, and light-collecting semiconductor elements from a wafer substrate to a destination substrate such as a display substrate. However, even for smaller iLEDs, problems with electronic control and mechanical support remain for tiled displays.
There is a need therefore for system architectures that enable smaller, higher resolution, lower cost, and higher performance tiles in a matrix-addressed system.